(1) Field of the Invention
This invention relates to a method for producing m-benzyltoluene. More particularly, the invention relates to the method for producing m-benzyltoluene with a high yield and good selectivity without producing undesirable heavier by-products.
(2) Description of Prior Art
There are three kinds of isomers of benzyltoluenes. The melting points of these three kinds of isomers are: p-isomer: 4.6.degree. C.; o-isomer: 6.6.degree. C.; and m-isomer: -27.8.degree. C. That is, the melting point of the m-isomer is extremely low. Incidentally, materials having lower melting points are preferred, for example, in the field of heat transfer medium or the like because of the easiness in starting machines and other advantages. Accordingly, the m-isomer is most desirable among the benzyltoluene isomers in view of low temperature characteristics.
As the method for producing benzyltoluene, it has been a principal method in the conventional art that a halide such as benzyl chloride is reacted with toluene (U.S. Pat. No. 4,523,044 and European Patent Publication No. 226,152). Meanwhile, for the method of disproportionation of diphenylmethane and toluene like the present invention, only the use of aluminum chloride has been proposed.
In addition, in another method which has already been proposed by the present inventors, benzyltoluene is prepared from toluene and diphenylmethane in the presence of disproportionation catalysts of a solid acid such as silicaalumina or a Lewis acid such as aluminum chloride (Japanese Patent Application No. 62-55863). In the case, however, that aluminum chloride is used as a catalyst, much heavier products and by-products such as ditolylmethane are formed and the yield of benzyltoluenes is not always good. The selectivity to m-benzyltoluene is also low. Furthermore, when a solid acid catalyst such as silica-alumina is used, the reaction also leads to similar results.
As the crystalline synthetic aluminosilicate zeolite, there are known several zeolites such as mordenite and Y-type zeolite. Nevertheless, it was found by the inventors of the present application that these conventional zeolites are not suitable for use in the method of this invention because they are short in catalytic life, in other words, the lowering of catalytic activity is severe and the shape-selectivity is low.
So many applications of so-called ZSM-5 family zeolites are reported by N. Y. Chen, et al. (CATAL. Rev. SCI. Eng., 28(2&3), 185-264 (1986)). Such a production method of m-benzyltoluene, however, has not been known.
Accordingly, it has been looked for to propose a novel method for producing m-benzyltoluene with a good yield and a high selectivity.